1. Field of the Invention
The present invention relates generally to the field of information storage devices, and more particularly to head gimbal assemblies that are used in information storage devices and that include a microactuator.
2. Background of the Art
Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all heads that can read are referred to as “read heads” herein, regardless of other devices and functions the read head may also perform (e.g. writing, flying height control, touch down detection, lapping control, etc).
In a modern magnetic hard disk drive device, each read head is a sub-component of a head gimbal assembly (HGA). The read head typically includes a slider and a read/write transducer. The read/write transducer typically comprises a magneto-resistive read element (e.g. so-called giant magneto-resistive read element, or a tunneling magneto-resistive read element) and an inductive write structure comprising a flat coil deposited by photolithography and a yoke structure having pole tips that face a disk media.
The HGA typically also includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the read head. The read head is typically bonded to a tongue feature of the laminated flexure. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, a rotary actuator, and a flex cable. The plurality of HGAs are attached to various arms of the rotary actuator, and each of the laminated flexures of the HGAs has a flexure tail that is electrically connected to the HSA's flex cable.
Modern laminated flexures typically include electrically conductive copper traces that are isolated from a stainless steel support layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flex cable on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along the actuator arm and ultimately attaches to the flex cable adjacent the actuator body. That is, the flexure includes electrically conductive traces that are electrically connected to a plurality of electrically conductive bonding pads on the head, and extend from adjacent the head to terminate at electrical connection points at the flexure tail.
The position of the HSA relative to the spinning disks in a disk drive, and therefore the position of the read heads relative to data tracks on the disks, is actively controlled by the rotary actuator which is typically driven by a voice coil motor (VCM). Specifically, electrical current passed through a coil of the VCM applies a torque to the rotary actuator, so that the read head can seek and follow desired data tracks on the spinning disk.
However, the industry trend towards increasing areal data density has necessitated substantial reduction in the spacing between data tracks on the disk. Also, disk drive performance requirements, especially requirements pertaining to the time required to access desired data, have not allowed the rotational speed of the disk to be reduced. In fact, for many disk drive applications, the rotational speed has been significantly increased. A consequence of these trends is that increased bandwidth is required for servo control of the read head position relative to data tracks on the spinning disk.
One solution that has been proposed in the art to increase disk drive servo bandwidth is dual-stage actuation. Under the dual-stage actuation concept, the rotary actuator that is driven by the VCM is employed as a coarse actuator (for large adjustments in the HSA position relative to the disk), while a so-called “microactuator” having higher bandwidth but lesser stroke is used as a fine actuator (for smaller adjustments in the read head position). Several microactuator designs and servo control recipes have been proposed in the art for the purpose of dual-stage actuation in disk drive applications.
However, the addition of one or more microactuators in a disk drive can be costly and troublesome. For example, the additional components of the microactuators add cost to the disk drive, as do the additional manufacturing steps required for fabrication and assembly of a disk drive that includes microactuators. Furthermore, the increased complexity of the actuation system can reduce disk drive manufacturing yield, and increase the frequency of disk drive failures during operation in the field. The increased development time to successfully implement a complex dual stage actuation system can delay product introduction, which may result in a significant opportunity cost to a disk drive manufacturer.
Therefore, there is a need in the art for a microactuator design that is useful for dual stage actuation in disk drive applications, and has acceptable cost and manufacturability for profitable high-volume production.